The Researching On Adaptive Resource Allocation In Multi-user OFDM System

With the development of the mobile communication technology, the OrthogonalFrequency Division Multiplexing (OFDM) system has become the hotspot. Itmodulates the signals to sub-carriers which are orthogonal and increase the time forsending signals, while reduce the effect of inter-symbol interference (ISI) effectively.The instantaneous channel gain of each sub-carrier is different in the real OFDMsystem. So if a fixed modulation scheme is applied to all sub-channels, the wholesystem's capacity and the transmitted power have not been full used. In this paper, adynamic resource allocation scheme is discussed. We divided the algorithms into twoparts, in the first part we discuss the algorithms used in the single user OFDM systemin which all the sub-carrier can be used by the only one. In the second part, we discussthe algorithms used in the multi-user OFDM system in which all the sub-carriers areshared by all users. A novel improvement algorithm is proposed under the optimaladaptive modulation for multi-user systems is introduced. It takes advantage of theinstantaneous channel gain in allocation properly with higher function with lowercomplexities. It also guarantees each user's request while arbitrate the subcarrierswhich are desired by several users. Simulation results show that the adaptivealgorithm has the similar performance as optimal technique in term of theory andoutperform static algorithms. Finally we introduced channel state information (CSI)error and CSI delay's influence on the performance algorithm for variable-rate OFDMsystems with imperfect channel information. We compared performance for the newproposed algorithm with that for traditional ideal algorithm ,then a direction to furtherimprove the performance is suggested.